Fusible salt pattern composition and process of making molds



KAZURO SUZUKI ETAL 3,131,999

May 5, 1 964 FUSIBLE SALT PATTERN COMPOSITION AND PROCESS OF MAKING MOLDS Filed March 9, 1960 i 3 F/EiJa- F/ELEa.

6 3,131,999. FUSIBLE SALT PATTERN COMPOSITION AND PRGCESS 6F MAKENG MOLDS Kazuro Suzuki, Nishinomiya-shi, Hyogo-lren, and Osamu Hiraiwa, lharagishi, sal a-fu,,iapan, assignors to Sunritomo' Kinzoku Kogyo Kahushiki Kaisha, Osaka-ski, Japan, a corporation of .lapan FiledManlP, 1960, Ser. No. 13,913

3 tllaims. (Cl. 22-496) This invention relates to precision. casting processes,

and to novel fusible pattern material to be used in the casting processes. 7

Wax casting processes are well known and widely practiced in many countries, but the wax pattern used'in the Y United States Patent O process has defects which are inherent in the material.

In view of the fact that the dimensional precision of the products has an immediate bearing on the precision of the wax pattern used, a variety'of difierent waxes of differing characteristics are known in the art. "Some commercial wax products are shown in Table I. I p v The manufacture of large type monoblock'castings such as blades for turbines and jet enginesis significan'tly afiected by such characteristics of the wax pattern asmoduli of solidification, contraction, 'thermal expansion, ,"deformation the, like, which results in dimensional. errors. For instance, in making a mold for a solid precision casting having a diameter of about 500mm. by using an available wax of a minimum thermal expansion coeflicient,

. thethermal expansion required for heating the wax to a TABLE I An object of the present invention is to provide a new fusible pattern material in substitution for wax.

It is another object of the present invention to provide a precision casting mold and a process for making the same by using the new fusible pattern material.

The above listed objects may be accomplished by using a new fusible pattern material composed of a mixture of organoalkali metal salt and alkali carbonate.

The organoalkali metal'salt according to the presen invention is composed of one or more than two kinds of salts selected from the group consisting of potassium salts and sodium salts of acetic acid, formic acid, oxalic acid,

citric acid and tartaric acid. Sodium acetate is preferred.

The alkali carbonate used'is either potassium carbonate or'sodium carbonate the latter being more suitable. The mixture is preferably composed of 80-60% by weight of 'organoalkali metal salt and 20-40% by weight of alkali carbonate. It is" preferredto form a crystalline hydrate b'y'mixing an organoalkali-metal salt containing proportion of abo'ut 20-40% thereto and the mixture is stirred well to'obtain a pattern material. a The necessary conditions of pattern material to be used for casting are enumeratedas follows:

(1) The melting point should be about l00 C. (2) Nochangein quality by heating. l

(3) Good pouring property. j I

(4) solidification with a minimum of shrinkage.

Characterzstzcs of Wax Surface Transhardness; Thermal Warp- Thermal Solidifi- Melting verse ,Martens detormaage Crystalexpancation Ash con- Kind point, strength, tester tion, 'mm. liuity sion,15 contractent,

1 C. kgJcm. Scratch 35 0. mm. 50 0.,- tion, percent width, percent percent Inlay wax 76.8 12.14 0.16 0.64' 1. 58 0.114 Ceresin 81. 9 1. 1' .0. 20. 10.64 0. 0.015 arafiin 61. 6 1. 16 0. 36 1. 25 0. 95 0. 005 D-8210W8JC (G. Br t.) 70.0 1. 77 0.14 1. 26 1. 44 0. 106 Armowax (U.S.'A.). 100.0. 5. 00 0117 1.36 No. 22 Yellow wax (U. 69. 8 s 1. 26 0.23 2.04

Casting wax'(U.S.A.) 70.6 6. 23' 0. 13 0.82 it D-144 Wax (U.S.A;) .'77.7 2.07 '0. 12 1.00 2.02 a 0.016 Rice bran wax} refined .;66. 2 A 1. 85 v0. 17 1.89 2. 22 0. 054 Wax, H-Co. (J'apan) 77. 0 1. 25' 0. 24 '1. 30 r 1. 38 0.019 Wax, K. Co (.lapan) 73.4 .-1..42 10.19 1. 40 0.050

y Wax 'patternsare usually made by-pouring wax into a 6d (5) It is readily removable lfromithe mold and does "not a metallic mold, solidifying' and then taking the formed pattern'ou'tof the mold. In such .a process, it is'necessary to give careful consideration to the thermal expansion, contraetiomwarpage, strain,1etc; of the wax, 'so, that a number gof testszare required.to predefermine. a correction value of wax relatiye to the metallic mold. into. which wax is. poured. ?;With all these; laborious andtime-consumirig efforts, the finished products are of uneven precision....m

casting. a

known defective; wax patterns-f for r f I r Y showninTable II.

act upon a mold releasing agentifz' (6) No deformation brsbfteningl. at room temperature as Well as having sufiicienthardness-and strength. Y '(7) A small thermal expansion coefficient (8). It does not act upon a mold binder.

(9) 'It=is easily. and promptly dissolved and remoyed, y. I (10 It is inexpensive. .1 1

conditions areiperfectly met-by aforenoted ture of salts according to the invention.

The ch acter of .the pattern made of the saltiis Patented May 5., 1964 3 TABLE II Properties of'Pattern Made of the Mixed 'Salt (i.e. a Mixture of 70% Crystalline Sodium Acetate and 30% Anhydrous Sodium Carbonate) Transverse strength,. kg.'/cm. 3.15.

:Surface hardness, Martens tester,

solidification expansion,;percent 0.05 (value relative to 7 the metallic mold). Thermal expansion (1-5+55' C,)

For making-a patternfrom said. material,x60-80%- of crystallinet sodium acetate .is' placed ,in a vessehand. dissolved .in its water of crystallization by meansof. a hot -bath,-.-and then .2040%-of powdered'anhydrous sodium carbonate is added thereto; ,The mixture is amplystirred -andtthen poured atabout 90-95" G. into a metallic mold. In 1-2 minutes after pouring, the pattern formed. can be easily removed. For making a number of patterns a .coolingmeans is provided forthe heated .metalliczmold, so that the mold can be; continuously operated to forma .patternzevery .1 2 minutes. .At the timeof pouring, the material, i.e. the mixed' salt needs no pressure .asrequired in the stagexofgpouring -or-solidifying wax. In addition, the pattern thus obtained has. advantagesin: that it accurately conforms to themetallic'mold eanddoesntcontract.

Inthe manufacture of a, precision casting moldiby making use of the pattern-produced as stated above,..the pattem is first coated with .a slip of'refractories containing such as a fused mixture of 60-80% CH COONa-3H O and 2040% Na CO This mixedsalt is neutralized with an acidic liquid and disappears, generating carbon dioxide gas. The velocity of dissolution in HClis approximately 6.0 mm./min. as shown inTable II. Thus, i

according to the present inventiona casting mold having a precision cavity can be manufactured with great ease.

The following example forproduction of a moldfora turbine blade is given to illustrate the process of the present invention with reference to the accompanying draw-.

ings in which: 7

FIG. 1a is a sectional elevation showing. one formo patternby .using the same mixed salt. gateisuseful for the vpattern ofvthe mixed salt to prevent means of a hot bath and then mixed with 30% of powdered. anhydrous sodium carbonate, and amply stirred. The mixed salt is poured at about 9095 C. into said metallic mold and set in l-2 minutes. Then, the split mold 1, 1' is separated to take out a blade type pattern formed. 7

In making a number of patterns by a continuous operation, the metallic mold becomes heated, whereupon the mold is cooled by a cooling liquid running through the chambers 4, 4'. The pattern made of the mixed salt differs from'conventional wax patterns in that no pressure is required in the pouring and setting stage and no error is caused by expansion due to heating or contraction due to setting, thus rendering it unnecessary to correct the metallicmold. .Thus,patterns true to the mold are obtained. InFIG. 1b is, shown a metallic mold for making a pattern of a feeder head, which comprises a slit mold 5,, 5' ,anda pouring. chamber. 6. By pouring said mixed .saltintolthe chamber 6, a feeder head type pattern is obtained. I

In FIG..,2a is shown, an assembly of the patterns removed .from themolds of FIG. la and FIG. lb. 7 is the blade type-patternand 8 is the feeder. head type pattern. Both patterns, are perfectly adhered to each other by the same 'mixed salt asha binder. A gate 9 made of chamotte, for-example, is'fitted to the feeder head type The chamotte its'immediate contact=with ahot iron plate as described afterwards. a I

' Theflnext .stepris tocoatthe pattern of FIG. 2 with an investment material of refractories. .For this purpose,.the method .for rapid setting of investment material (as dis- .closed e .g. in Japanese. Patent No. 240,080) is most suitable,,because"the.,pattern is water-soluble. To prepare an investment, 50 cc. ofethyl silicate are stirred and then ,10 cc. of a dilute solution of 0.5% hydrochloricacid are added thereto therebymaking a silicasol. By adding about 100 cc. of water to the sol, anaqueous plastic sol is formed. A slurry of refractories, i.e. a mixture of said .plastic s'olrand about '600gms. of powdered aluminium .oxide, is.appliedto the surface of the pattern by dipping or coating. This slip is immediately gelated and set within lOseconds by contacting with gaseous ammonia. The operation is repeatedly carried out, until a shell of i suitable thickness is formed on the surface of the pattern.

FIG. 3 shows, in.cross-section,.a refractory shell 10 thus formed over the pattern 7, 8.

If desired, the pattern coated with the investment can be reinforced with so-called backup. As shown in FIG.- 4,-a. base plate 12 is adapted to be longitudinally vibrated by means of a shaking device 11. The pattern is placed on saidplate 12 with the chamotte gate 9 facing down, and surrounded by a metal flask 13 in which the sand 14 mingled with organic syntheticresin is filled whilethe plate' 12 is longitudinally vibrated. The plate .112 and the flask 13 are heated at 230-280 C. so that a a metallic mold for making a pattern;

FIG. lb shows in sectional elevation another form of .mold; e V I FIG. 2a is a sectional elevation showing an assembly of the pattern;

FIG. 2b is a cross section on line II-II of FIG. 2a.

FIGQS is a sectional elevation-of the pattern coated with an investment material; 1

FIG. 4 is asectional elevationillustratingone form of the production of a casting mold;

FIG. 5 is a sectional elevation of a finished casting mold.

Referring to'FIG. -la, therein isJshownariretallic' mold for a blade type pattern, which comprises. a slit mold 1, 1', a pouring chamber 2, an inlet 3 and cooling chambers 4, 4'. Firstly, apattern is made of a mixed salt. For example of crystalline sodiumacetate is placed in a vessel and dissolved in its own-water-of crystallizationby portion of the sand 14 comes in contact therewith and is promptly set.

"larly heated, a portion of the sand '14is also set.

On touchinga pressing plate 16 simi- Thus, the setsand layer 15 is formed around the shell, and then the plate'12,-the pressingplate 16 and the flask 13'are approximately double the time for dipping in'an acidic solution.

The washed mold is dried at about 200 to 250 C. The necessary tirnefor drying the mold of said type is about Z'hours, but, of course, it varies with the size of mold. During the course of drying, a still unset portion 14 of the reinforcement sand (FIG. 4) is finally set. The finished casting mold is shown inFIG. 5.

As clearly seen from What has been described, the present invention is superior to the prior art, in that a pattern perfectly true to the original metallic mold can be manufactured with great ease, Without producing any error with respectrto expansion, shrinkage, strain etc. Furthermore a pattern can be made in 1-2 minutes without requiring pressure and promptly coated with an investment. Moreover, the dissolution of the pattern thus made, and the washing and drying of the finally formed casting mold can be effected in such a short time and in such a simple Way as cannot be expected from the known art while finally the final product excells the known products in dimensional precision.

What is claimed is:

1. A composition of fusible and soluble pattern material for making precision casting molds, said composition consisting of a mixture of 60 to 80% by weight of 6 crystalline sodium acetate and 20 to by weight of anhydrous sodium carbonate.

2. A process for the production of precision casting molds comprising mixing to by weight of crystalline sodium acetate and 20 to 40% by weight of anhy drous sodium carbonate, pouring the thusly obtained mixture intoa metallic mold and solidifying the mixture to form a pattern corresponding in shape to that of the mold, removing the pattern from the mold and coating the pattern with a refractory shell, and dissolving said pattern to leave the refractory shell in the form .of the mold.

3. A process as claimed in claim 2, wherein the refractory shell is formed by coating the surface of the pattern with a slurry of refractories which contains silica sol as a binder, and then setting said coating by contacting the same with an alkaline gas.

References Cited in the file of this patent UNITED STATES PATENTS 2,136,077 Bartlett Feb. 28, 1956 2,754,570 Crawford July 17, 1956 2,992,995 Arden July 18, 1961 OTHER REFERENCES Transaction of the American Foundrymens Society, vol. 64, May 3-9, 1956, pages 504-508. 

2. A PROCESS FOR THE PRODUCTION OF PRECISION CASTING MOLDS COMPRISING MIXING 60 TO 80% BY WEIGHT OF CRYSTALLINE SODIUM ACETATE AND 20 TO 40% BY WEIGHT OF ANHYDROUS SODIUM CARBONATE, POURING THE THUSLY OBTAINED MIXTURE INTO A METALLIC MOLD AND SOLIDIFYING THE MIXTURE TO FORM A PATTERN CORRESPONDING IN SHAPE TO THAT OF THE MOLD, REMOVING THE PATTERN FROM THE MOLD AND COATING THE PATTERN WITH A REFRACTORY SHELL, AND DISSOLVING SAID PATTERN TO LEAVE THE REFRACTORY SHELL IN THE FORM OF THE MOLD. 